Diversity receiving system



July 4, 1950 Filed March 30, 1944 W. l. MATTHEWS DIVERSITY RECEIVINGSYSTEM RF. AMPLIFIER.-

CQNVEM'ER. LF. AMPLIFI J RE AMPLIFIER CONVERTER.

IF AMPLIFIER.

lAl IIIIIII L OAD ATTORNEY.

3 Sheets-Sheet 1 July 4,- 1950 w. I. MATTHEWS DIVERSITY RECEIVING SYSTEMI 3 Sheets-Sheet 2 Filed March 30, 1944 Fig. 2.

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' WALTER I. MATTHEWS.

s7 5 RECEIVER I BY ATTORNEY.

y 4, 1950 w. 1. MATTHEWS 2,513,811

DIVERSITY RECEIVING SYSTEM Filed March 30, 1944 6 Sheets-Sheet 3 Fig. 3.

RFAMPLIFIER CONVERTER.

LEAMPLIFIER.

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INVENTOR. WALTER I. MATTHEWS.

BY QQW ATTORNEY Patented July 4, 1950 DIVERSITY RECEIVING SYSTEM WalterI. Matthews, Riverhead, N. Y., assignor to Radio Corporation of America,a corporation of Delaware Application March 30, 1944, Serial No. 528,748

9 Claims. (01. 250-20) This invention relates to diversity receivingsystems, and more particularly to that type of radio receiving equipmentwhich makes provision for combining the signal energy derived fromdifferent antennae and separately amplified in different radio receivingcircuits.

In order to mitigate the effects of fading, which is encountered inradio signals generally, it has been the practice heretofore to make useof as many as three radio receivers each fed by geographically spacedantennae. The output of each receiver is rectified and the differentrectified outputs from the several receivers are fed into a common loadresistor. The voltage across the common load resistor is called thecombined output and this voltage is fed to any suitable utilizationdevice.

I have found that certain economies may be effected in diversity systemsif it is not convenient to employ as many as three receiving antennae.In certain adaptations of my invention, it is also possible to reducethe number of complete receiving sets to be used in diversity reception.

Experience ha shown that fading elimination is to a large extentproduced by combining the output of two receivers. The addition of athird receiver further improves the overall reception to such an extentthat the cost of the additional third unit of equipment has heretoforebeen con sidered well warranted.

It is an object of my invention to provide circuit arrangements forcombining the effects of signal reception at fewer than three antennastations, while at the same time obtaining a close approximation to thediversity effects of signal pick-up at three geographically spacedpoints.

It is another object of my invention to provide diversity receivingequipment of simplified design so arranged that when two antennas areused, the signal energy thereby collected may be amplified in two ormore receivers and applied concurrently to a common load.

It is another object of my invention to provide receiving equipmentsuitable for obtaining a close approximation to three-set diversity eventhough a single antenna array is used, such as that which is shown in mydiversity antenna U. S. Patent No. 2,186,422, which issued January 9,1940.

My invention will now be explained in more detail, reference being madeto the accompanying drawings, in which:

Fig. 1 shows schematically a circuit arrangement including two sets ofamplifier and converter stages in a diversity receiving system andarrangements for combining the outputs rrom these stages throughdifferent amplifier and rectifier circuits so as to obtain substantiallythe effects of a three-set diversity system;

Fig. 2 shows a modification of my invention in which two geographicallyspaced antennae are used and the energy collected thereby is fed througha novel circuit arrangement designed to combine the separately collectedsignal energy components in aiding phase relationship;

Fig. 3 shows another modification of my invention in which two antennasand two sets of amplifier and converter stages are used and the outputfrom the two sets is combined by the use of as many as four detectorcircuits; and

Fig. 4 shows a system for coupling the input circuits of two receiversto a single antenna array of special type, the object being to obtainthe advantages of a diversity receiving system.

Referring first to Fig. 1, I show therein two signal translating sets Iand 2, each of which is provided with an antenna 3 and each including aradio frequency amplifier, a converter, and an intermediate frequencyamplifier. These translating sets are provided with an automatic gaincontrol device, as will hereinafter be explained.

It is well known that fading efiects can be reduced by the use ofgeographically spaced antennae the signal waves from which are fed intoseparate receivers. Multipath radiations produce random fading effectswhich ordinarily are not simultaneous at different antennae. Thesefading effects are accompanied by random phase relations between thesignal waves coming in to a single antenna on two or more paths, andalso between the signals collected by difierent antennae. Phasedifferences are carried through the receiver circuits up to the finalstage of detection of the intermediate frequencies. Therefore, attemptsto combine the signals before rectification have usually beenunsatisfactory. The operation of combining the signal energies afterrectification is, however, entirely satisfactory, since phasedifferences in the carrier waves are entirely nullified in the rectifiedoutput across the load resistor.

The circuit arrangement of Fig. 1 not only provides for combining therectified output from each of the two translating sets I and 2 in aconventional manner, but, additionally, the outputs of these sets arecombined before rectification and fed to a third detector whichultimately delivers output energy for combining with the output from theother two detectors. All three detectors feed to the common load.

Translating set i has its output circuit connected to the control gridsin each of two amplifier tubes 4 and 5. Likewise, translating set 2 hasits output connected to the control grids of two amplifier tubes 6 andl. Tubes 4 to 1 inclusive are preferably of the pentode type, althoughother types of tubes may be used if desired. The circuits of these tubesare conventionally shown, and it will be understood that for the sake ofsimplicity in the drawing, I have omitted all showing of the usualbypass condense-rs and other elements of circuit refinement since thechoice of these elements may readily be made by those skilled in theart,and-my-invention does not depend for its novelty upon any particularchoice.

The output circuit of tube. 5. includes. the primary winding of atransformer S. This winding is shunted by a tuning capacitor 9. Theoutput circuit of tube 1 is similarly arranged and includes the primarywinding of-a transformer ii! which is also tLmed-by-meansof theadjustable capacitor ll. i

The output-circuitsof tubes-'fi-and-fiare joined together and have acommon interstage coupling transformer 12. The "primary winding of thistransformer is tuned by-'means-of the adjustable capacitor 13.

Each of the-secondaries of transformers- 8,- i9, and I2 iscentertappedin order to provide-circuits for full-wave rectification theterminals of these secondariesare connectedrespectively to individualanodes in-difierent twin diode rectifier tubes I4; l5, and-i6.Thecommoncathodes-in all of these tubes are grounded. 'Each ot thesecondary windings of "transformers 8, and I2 is also tunedby means-ofadjustable capacitors I1.

A common loadresistorifi -is connectedat one end ,to ground and at theother end to a combining circuit conductor '38 which is fed -withrectified signal" energy -from'- the 'severalcentertaps-of the secondarywindings in transformers NHL-and 12. In-circuit with-these connections,however, I preferably -employ -high frequency chokes I 9, the terminalsofwhich are Y associated with condensers-2 I] for bypassing-highfrequency components to ground.

"The terminals of' the load'resistor 48' may be connected to anyutilization device, not shown.

AtapZI "on the load resistor-providesconnection at a suitable pointforderiving the desired AVC potentials. These :potentials are fed through atime constant-circuit 'consisting of resistor 22 andgrounded capacitor23. The

AVC' potentials are 'thenapplied through conductors 24 to the inputcircuitswithin the translating sets land 2.

It will be understood that whenever the" phase relation existingbetweenthe outputvoltagesin translating sets-tand- 2'is additive in-efiect;then the-combining of output energies from tubes-5 l and -6'wil1producea considerable addition to the the phase relation between thesignals as received at the two separate points is favorable.

At other times the normal conditions of diversity -reception for-pickaupat two receiving points. are

automatically met.

Referring nOW to Fig. 2, the modification .Lthereinflshown ;is one inwhich two antennas 3a and 3b, are provided. In this modification,however,'I use three complete radio receiving sets 25, 26, and 21.Receiver 2-5 is fed with energy from antenna 3a. --Receiver 2'! is-fedwi-thenergy -from antenna 32). Antenna -circuit-connectionsare alsomade-to the receiverdti through-anelectronic combiningcircuit wherebysignal energies derived from 'both antennas 3a and I 3b are utilized.The combiningcircuit inoludesradio frequency transformers 28 and 29.The-primary -coils of these transformers --are connected -respectivelyto-antenna'fia-and antenna -31). The secondariesof transformers-28 and=29 are tuned by-means of adjustable capacitors -30.

'An' amplifier tube A 3 l --has-its 1 control grid connected to oneterminalof the secondary or transformer 28-. Likewise-another amplifiertube 32 has its control grid connected tooneterminal of the secondary-oitransformerfiZ-B.

Tubes 3! and 32 are preferably pen-todes, although other types ofamplifier tubes may be used -'if-desired. Screengrid potentials arederived from the usual-direct current operating sourceand -fed throughvoltage dropping resistors 33.

Each of the-receivers'25, 25,-and 21 is provided with an input circuitwhich preferably includes the tuned secondary winding ofa-couplingtransformer. 'These transformers are indicated for therespectivereceiversat'34, 35,'and 36. Transformer-34-couples antenna 30.to the input circuit of receiver'25. Transformer-35 has its primarywinding common to thebutput circuits of tubes '3 l and 32. Transformer36- hasits-primary winding connected-to; antenna 3b.

Each of the receiving" sets" 25,16, and-21' is equipped "with "the usual.full-wave 'detector. 'Rectified signal potentials derived from "thesedetectors are combined and fed-through conductor38 to-thecommon load-3i.The terminals of this ioad may .be "used to supply useful energy toany-desired utilization device.

Each of the receivers 25,16, and 27 ispreferablyequipped with anautomatic volume control circuit. The AVC--p0tentials, are derivedfromxa tap 2! ,on the common load and fed through a time constantcircuitincluding resistor '22-and capacitor-'23; the same as shown-inFig. 1.

Inthe operation of the "embodiment of my in.- -vention shown in Fig;2,,antenna 3a, ,feedssimuI- taneously to receiver'25 and to the couplingtube 3!. Antenna 3b likewise feeds simultaneously, to receiver-21 andto---the;couplin :tube32. Since theanodes of the two couplingtubes-'3I-and 32 are both connected to the primary or transformer -35 it willbeunderstood thatreceiver 2 6- is subject to control-by" both antennas 3a"and 3b. "If the phase-relationbetween the high-frequency signalsreceivedon the two antennas isfavorable, then receiver 26 contributes to aconsiderable extent in the elimination of fading. When the phaserelations are unfavorable for such reception, then either receiver orreceiver 21 provides maximum output and this output is used to theexclusion of the output from the other receivers, due to the inherentaction of the fullwave rectifiers.

Referring now to Fig. 3, I show still another modification wherein twoantennas 3 are used. Each of these antennas delivers its collectedenergy to one or the other of two translating sets I and 2, the same asshown in Fig. 1. The method of utilizing the output from the two sets Iand 2 is, however, quite different from that which is shown in Fig. l.

The output from the last stage of intermediate frequency amplificationin translating set I is coupled to control grids in each of threecoupling tubes All, 4!, and 4-3. The output fromthe last stage ofintermediate frequency amplification in set 2 is likewise connected tocontrol grids in each of three coupling tubes 42, M, and 45. The purposeof the different tubes M to 45 inclusive is to provide combining effectswhich serve to meet all possible conditions of phase relation shipbetween the high frequency signals derived from the two translating setsI and 2. This will be explained in more detail after completing thedescription of the circuit arrangement.

The output circuit of tube id is one which includes the primary windingof a transformer 45. The secondary winding of this transformer iscentertapped while its terminals are connected to the anodes of afull-wave rectifier 58.

The anodes in tubes 4! and 42 are interconnected and the combined outputsignals are fed through the primary winding of transformer fill.Coupling tubes 43 and 44 are arranged for pushpull output, their anodesbeing connected to opposite terminals of the primary in transformer d8.This primary has a centertap feeding direct current operating potentialsto the anodes. Coupling tube 45 functions in the same manner as couplingtube Mi, but tube 45 is controlled by output energy from translating set2 and rectification of this energy is provided in the full-waverectifier tube 53 which is fed from the secondary of transformer 49.

Each of the rectifier tubes 5% to 53 is of the twin diode type. Thecommon cathodes are grounded. The centertaps on the secondaries oftransformer 46 to 49 inclusive are connected to the common load 31through high frequency chokes 19. Bypass condensers iii are used todrain off to ground the unwanted high frequency potentials in thedetection circuits.

In the operation of the circuit arrangement as shown in Fig. 3, couplingtubes 4!] and 45 in association respectively with rectifier tubes 5!]and 53 provide conventional diversity reception. Supplementing this, Iprovide for the combining of signal potentials from the translating setsI and 2 when their phase relations are additive, the combining actiontaking place through coupling tubes M and 42. Rectification is providedin the diode tube 5!.

I also provide for increasing the useful output from translating sets Iand 2 when the phase relations between high frequency energies areopposed. In this case, coupling tube 43 is controlled by set i andcoupling tube 44 is controlled by set 2. Since tubes 43 and 44 operatein pushpull relation, the combined output applied to the variable in anunpredictable manner.

rectifier 52 is favorable to the differently phased signals.

Whenever the voltages derived from translating sets I and 2 differ lessthan in phase, they contribute their energies largely through pentodetubes 4| and 52 to the full-wave rectifier 5i. Voltages diifering morethan 96 are added by using the coupling tubes 23 and 44 in push-pullrelation so that the output therefrom may be rectified in tube 52.

Fig. 4 shows how my invention may be modified so as to be suitablyemployed in connection with a single antenna array such as shown in myU. S.

Patent No. 2,186,422. The antenna array of the patent is arranged toreceive horizontally and vertically polarized radio waves and todistinguish the same by assigning their energies respectively to twoindependent transmission lines.

In Fig. 4, therefore, I show an antenna array 63 having the generalshape of a half diamond and having a plurality of dipole arms 64. Thetwo conductors of the transmission line are connected to the terminalsof an inductance coil Receiver i has its input circuit connected tothese terminals. A midtap on the coil 65 is connected to ground throughthe primary winding 6? of a transformer iii). The secondary winding 68of this transformer is connected to the input circuit of receiver 2.

As explained in the patent, when the horizontall polarized signalspredominate, the end terminals of coil 65 will experience voltages ofopposite polarity, thus transferring signal energy to receiver I, whileno difference of potential will exist between the centertap and ground.Thereiore, none of the energy due to the horizontally polarized signalwaves will appear across the secondary iii; of transformer 66. Forvertically polarized waves the end terminals of coil 65 receive voltagesof like polarity, thus resulting in no energy transference to receiveri. These like voltages, however, give rise to a potential differenceacross the transformer primary 6"! and thus result in the transfer ofenergy to receiver 2.

Since the polarization of the incoming signal wave may assume any anglewhatsoever, and since this angle varies from time to time, it followsthat the ratio between the horizontal and vertical components of thesignal energy is So it will be appreciated that reception by one of thetwo receivers will dominate over that of the other except when the twocomponents of polarization are substantially equalized; that is, whenthe axis of polarization assumes an angle of 45 with respect to the axisof the dipole antenna arms.

My present invention meets this condition advantageously, and theembodiment shown in Fig. 1 is most efficient in smoothing out theresponse. Considering the operation of Fig. 1 as applied to Fig; 4,then, as the axis of polarization rotates from horizontal to vertical,the output from translating sets l and 2 will be rectified first in tubei i. Then it will be gradually shifted into tube [5, and finally intotube l5. Throughout this rotation of the polarization axis the rectifiedsignal energy will be continuously applied to the common load it and tothe utilization device.

My invention is, of course, capable of modification in various waysother than as indicated by the illustrative embodiments herein shown anddescribed and without departing from the spirit and scope of theinvention itself.

aieraan of said-intermediate frequency amplifiers, asecnd pair ofdischarge devices having inputelectrodes :likewise coupled in parallel.to..-the.- output terminals 'of the other-of said.intermediateefrerquency. .ampilfiers two ifullwaverectifiers, acouplingbetween. one. .fullewave rectifier and one device of. one pair-.of.devices, .a. ,couplingbetween the other full-wave rectifier and. onedevice. of

the other pa-irof devices,.a thirdfulL-Waverectifier, coupled .to thetworemaining dischar e; .devices, .in. parallel, and. a common load towhich rectifiedsienalp t ntials from all three rectifierszare. fed...

.2. .Inadiversityreceiving yst m, wo separate antennae, three receivingsets two of which are individual. ,to each, antenna and the third ofwhich receptive of signal energy derived from both antennae, anelectronic combining circuit for translating signal energy from the twoantennae to said third receiving set, a detector in each receiving set,and a common load for all three detectors.

.3. In a diversity receiving system, two separate antennae, a receivingset individual to each antenna, each receiving set including a radiofrequency amplifier, a converter, andv an intermediate frequencyamplifier, three dis.- charge deviceshaving their input circuits coupledin parallel. to the output from one of said intermediate frequencyamplifiers, three other discharge devices having their input circuitssimilarly coupled in parallel to the output from the other of saidintermediate frequency amplifiers, .four full-wave rectifiers coupledto-the out- ,put circuits of said discharge'devices in a particularmanner and arrangedto feed their rectification products to a commonload; said par- 'ticularmann'er of coupling beingsuch-that each of tworectifiers derives signal energy-exclusively from a respective one ofsaid antennae, a third one of said rectifier-s derives signal energiesfrom-both antennaewhen thephase-relation-between such energies produces.an additive effect by push-push action intwo certai-nones-of saiddischarge devices the output circuits of. which are connectedinparallelto said third rectifier,

and afourth one of saidrectifiers derives signal energies from-bothantennae when a contra.-

phasal-relation between such-energies favors push.- pull action inanother pair of-said discharge devices 'theoutput circuits .of whichare. opposingly-coupled to saidifourtlrrectifien.

L. A diversity receivingsystem having two receiving channels, twodetecting circuits each in- :dividual tor a: respective receivingchannel, at least one detecting, circuit under joint control of signalenergies simultaneously derived from the tworeceiving channels, and a.utilization circuit coupled, in common to-theoutputsofall said detectingcircuits in such manner. that the strongest. signal passing through anyof. said :detectingcircuits produces adominatingeffectuponrsaid'utilizationcircuit.

5.. A diversity receiving system according to claim .4 wherein each ofthe detecting circuitsis coupledrespectively to. the output of adifferent receiving circuit possessing stages of radio frequencyamplification, conversion and intermediate frequency amplification, andan amplifier stageis coupledto both of said receiving channels ahead. ofthe receiving circuit which feeds signal energies to saidaone detectingcircuit.

6.. A. .diversity receiving system according to c1aim, 4 and includingtwo twin diode detecting circuits to which signal energies aresimultaneously applied from both. receiving channels, one of saiddetecting circuits being fed with such energies through a push-pushamplifier and the other of said detecting circuits being fed with suchenergies through a push-pull amplifier.

7. A diversity receiving system having two receiving' channels; eachincluding a radio frequency-amplifier, a converter and anintermediate-frequency amplifier, the output from each I. F. amplifierbeing connected to the input terminals. of a- :pair of separateamplifier stages, means for separately rectifying the output from oneamplifier stagein each pair, means for combining the. outputs from theother two amplifier stages of said pairs, means for rectifying saidcombined outputs, and a common load impedance across. which thepredominant rectified signal energy-is impressed as derived from any oneof zthegthree saidrectifying means.

8;. Ina diversity receiving system wherein signal energy is collected bytwo geographically spacedxantennas, a plurality of signal translatingsets including means for separately amplify- .ing the energy. collectedby each antenna, means for-firstvcombining and thereafter rectifyingenergies collected'by the-two antennas, other means forseparatelyrectifying energy from each respective antenna, and a commonload intowhich all of the rectified energies are-fed.

9. 'A diversity receiving system as defined in clainr4 wherein eachdetectingcircuit comprises a twin diodeelectron.discharge'device andwhere- .in. said one detecting circuit under joint control is soconnected to both receiving channels that the output thereof produces adominating elfect upon-said utilization circuit when the signal-energies appliedto said. one'circuit from the two channels, aresubstantially in phase with each other.

WALTER I. MArT EWs.

REFERENCES omen The following references are of record in the file. ofthis patent:

UNITED* STATES PATENTS Number Name Date 1,698,014. Falkner Jan. 8, 19291,719,845 Martin. July 9,, 1.929 1,874,866 Beverage W Aug. 30, 19321,904,772 Taylor Apr. 18, 1933 2,364,952 Crosby Dec. 12, 1944 2,448,866Crosby Sept. 7, 1948

